Method for measuring activation energy of lithium ion battery

Abstract

The invention belongs to the technical field of battery detection, and relates to a method for measuring activation energy of a lithium ion battery. The method aims at solving the technical problems that an existing lithium ion battery activation energy measuring method depends on equivalent circuit fitting or relaxation time distribution analysis, model selection and parameter setting have high subjectivity, consequently, an activation energy calculation result is unstable and poor in repeatability, a data processing flow is complex and time-consuming, and rapid analysis and large-scale application are not facilitated. The invention provides a method for measuring activation energy of a lithium ion battery, which comprises the following steps of: performing sweep frequency impedance test on the lithium ion battery at different temperatures to obtain impedance spectrum data at corresponding temperatures; based on the impedance spectrum data, determining the frequency corresponding to the maximum absolute value of the impedance imaginary part as a characteristic frequency value at the temperature; and establishing a relational expression that the characteristic frequency changes along with the temperature, and calculating the activation energy and pre-exponential factors of the lithium ion battery according to the relational expression, thereby realizing rapid, accurate and high-stability measurement of the activation energy.

Description

Technical Field

[0001] This invention belongs to the field of battery testing technology, specifically relating to a method for measuring the activation energy of lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries are widely used in consumer electronics, electric vehicles, and energy storage systems. Their electrochemical performance is largely limited by the kinetic characteristics of ion transport processes within the battery. Activation energy, as a crucial parameter characterizing the ease of ion migration, is closely related to the battery's rate performance, cycle life, and low-temperature characteristics. Therefore, accurately determining the activation energy of lithium-ion batteries has significant engineering and research value.

[0003] Currently, activation energy is typically determined using electrochemical impedance spectroscopy (EIS). This method involves measuring the impedance changes of the battery at different temperatures and then fitting the relationship between temperature and kinetic parameters using the Arrhenius relation to obtain the activation energy. Existing research often bases activation energy on equivalent circuit parameters such as charge transfer resistance and diffusion impedance. These parameters are obtained through equivalent circuit fitting, and the activation energy is then calculated based on their temperature-dependent trends.

[0004] However, the existing technology has the following main problems: (1) The results are not unique due to the dependence on equivalent circuit fitting: different fitting models and initial value settings will affect the fitting results, making the calculation of activation energy unstable and highly subjective.

[0005] (2) The fitting process is complex and the repeatability is poor: There are many equivalent circuit parameters, the fitting process is time-consuming and easily affected by noise, resulting in poor test repeatability.

[0006] (3) Lack of direct measurement methods based on frequency domain characteristics: Existing methods mostly rely on the temperature change law of a certain impedance element in the equivalent circuit, rather than directly using the characteristic points of the impedance spectrum for characterization, which limits the simplicity and reliability of the test.

[0007] Therefore, there is an urgent need for a measurement method that does not require complex equivalent circuit fitting and can directly determine the activation energy based on impedance spectrum feature points, so as to improve the stability, accuracy and repeatability of activation energy testing. Summary of the Invention

[0008] 1. The technical problem the invention aims to solve. To address the problems of existing methods for measuring the activation energy of lithium-ion batteries, such as reliance on equivalent circuit fitting or relaxation time distribution (DRT) analysis, highly subjective model selection and parameter setting leading to unstable and poor repeatability of activation energy calculation results, complex and time-consuming data processing procedures, unfavorable for rapid analysis and large-scale application, and failure to fully utilize characteristic frequencies with clear physical meaning in the impedance spectrum, making the activation energy acquisition indirect and susceptible to noise, this invention provides a new method for measuring the activation energy of lithium-ion batteries.

[0009] 2. Technical Solution To achieve the above objectives, the provided technical solution is as follows: Based on the purpose of this invention, this invention provides a method for determining the activation energy of a lithium-ion battery, comprising the following steps: S1. Perform frequency sweep impedance testing on lithium-ion batteries at different temperatures to obtain impedance spectrum data at the corresponding temperatures; S2. Based on the impedance spectrum data, determine the frequency corresponding to the maximum absolute value of the imaginary part of the impedance as the characteristic frequency value at that temperature; S3. Establish the relationship between characteristic frequency and temperature, and calculate the activation energy and pre-exponential factor of lithium-ion battery based on the relationship.

[0010] According to any embodiment of the first aspect of the present invention, the method for determining the activation energy of a lithium-ion battery, wherein the frequency sweep impedance test has a frequency sweep range of 0.01 Hz to 1,000,000 Hz.

[0011] The frequency sweep range of the swept impedance test is limited to 0.01 Hz to 1,000,000 Hz, ensuring that the characteristic frequency falls within the test range, thus enhancing the effectiveness and repeatability of the test; it also avoids characteristic frequency measurement deviations caused by improper frequency selection, thereby improving the reliability of the method.

[0012] According to any embodiment of the first aspect of the present invention, in the method for determining the activation energy of a lithium-ion battery, when the frequency corresponding to the maximum absolute value of the imaginary part of the impedance falls at the boundary position of the frequency scanning range, the frequency scanning range is adjusted and the frequency sweep impedance test is performed again.

[0013] For cases where the characteristic frequency appears at the boundary of the frequency scanning range, operational steps for readjusting the scanning range are provided to ensure that the characteristic frequency can be accurately measured; this improves the applicability and flexibility of the method under different battery and temperature conditions.

[0014] According to any embodiment of the first aspect of the present invention, the method for determining the activation energy of a lithium-ion battery involves establishing a functional expression in which the characteristic frequency and temperature satisfy an Arrhenius relation, linearizing the functional expression, and calculating the activation energy and pre-exponential factor based on the slope and intercept of the linearized expression.

[0015] The Arrhenius function is clearly established between the characteristic frequency and temperature and linearized to make the calculation of activation energy and pre-exponential factor more direct and accurate; the cumbersome curve fitting process is avoided, improving data processing efficiency; and a scientific and reasonable calculation basis is provided, facilitating comparison and analysis under different experimental conditions.

[0016] According to any embodiment of the first aspect of the present invention, the method for determining the activation energy of a lithium-ion battery involves performing a sweep frequency impedance test on the full battery at different temperatures to obtain the characteristic frequency of the full battery, and calculating the activation energy of the full battery based on the relationship between the characteristic frequency and temperature.

[0017] The activation energy of a full cell is obtained by measuring its characteristic frequency, which facilitates the evaluation of the overall performance of the cell. It also allows for rapid batch testing of different cells, improving testing efficiency and data consistency.

[0018] According to any embodiment of the first aspect of the present invention, a method for determining the activation energy of a lithium-ion battery involves constructing a corresponding half-cell for a positive or negative electrode, performing a sweep impedance test on the half-cell at different temperatures to obtain the characteristic frequency of the positive or negative electrode, and calculating the corresponding activation energy based on the relationship between the characteristic frequency and temperature.

[0019] Measuring half-cells constructed from positive or negative electrodes allows for the acquisition of electrode activation energy, facilitating the analysis of electrode material kinetics; it provides quantitative data support for new material evaluation, electrode modification, or electrolyte optimization; the method can decompose the overall battery kinetics, which is beneficial for a deeper understanding of battery performance limiting factors.

[0020] According to any embodiment of the first aspect of the present invention, the method for determining the activation energy of a lithium-ion battery, wherein the swept impedance test uses an AC disturbance signal with an amplitude not exceeding 10 mV to ensure that the test process is in the linear region.

[0021] An AC disturbance signal with an amplitude not exceeding 10 mV is used to ensure that the test is carried out within the electrochemical linear range, avoiding measurement errors caused by nonlinear effects; this improves the accuracy and reliability of the activation energy determination results.

[0022] According to any embodiment of the first aspect of the present invention, the method for determining the activation energy of a lithium-ion battery includes at least three temperature ranges in step S1, and the interval between adjacent temperatures is no greater than 10 °C.

[0023] Setting at least three temperature levels and ensuring that the interval between adjacent temperatures is no more than 10 °C guarantees the sufficiency of data points required for fitting the Arrhenius relation and the accuracy of the fitting; it also improves the accuracy of activation energy calculation and experimental repeatability.

[0024] According to any embodiment of the first aspect of the present invention, the method for determining the activation energy of a lithium-ion battery, wherein the temperature range of the swept impedance test is -25 ℃ to 60 ℃.

[0025] The test temperature range is limited to -25 ℃ to 60 ℃, which is within the safe operating range of lithium-ion batteries; this allows the method to be used for battery performance evaluation under actual operating temperature conditions, while avoiding damage to the battery caused by low or high temperatures.

[0026] According to any embodiment of the first aspect of the present invention, the method for measuring the activation energy of a lithium-ion battery is a lithium-ion battery that is charged and discharged using a lithium-ion intercalation / deintercalation mechanism.

[0027] The method clearly defines the lithium-ion battery type as a lithium-ion battery employing an intercalation / deintercalation mechanism, ensuring a clear scope of application; it avoids the inapplicability of the method to non-lithium-ion batteries, thereby improving the enforceability and specificity of the claims.

[0028] Any embodiment of any aspect of the present invention can be combined with other embodiments without contradiction. Furthermore, in any embodiment of any aspect of the present invention, any technical feature can be applied to the same technical feature in other embodiments without contradiction.

[0029] Without causing contradictions, any technical feature of any aspect or embodiment of the present invention is equally applicable to any other embodiment or embodiment of any other aspect. Of course, when applicable to each other, appropriate modifications may be made to the corresponding features as necessary. The various aspects and features of the present invention are further described below.

[0030] 3. Beneficial effects Compared with existing known technologies, the technical solution provided by this invention has the following beneficial effects: The method for determining the activation energy of lithium-ion batteries disclosed in this application provides a method based on the characteristic frequency of swept impedance, which eliminates the need for equivalent circuit fitting or DRT analysis, thus avoiding the influence of subjective human factors on the results. It can directly extract the characteristic frequency from the impedance spectrum, improving the accuracy and repeatability of activation energy calculation. The method is simple and the testing steps are clear, enabling rapid acquisition of activation energy data at different temperatures, making it suitable for rapid analysis in laboratories and production lines. Simultaneously, it yields the pre-exponential factor, providing more parameter support for battery kinetic analysis and temperature-dependent performance prediction. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of a process for determining the activation energy of a lithium-ion battery, provided as an embodiment of this application. It illustrates the overall steps from swept-frequency impedance testing to characteristic frequency extraction and activation energy calculation.

[0032] Figure 2 This is a schematic diagram of data for obtaining the characteristic frequency of a graphite electrode at different temperatures, provided as an embodiment of this application. It shows the curve of the imaginary part of impedance changing with frequency and the characteristic frequency corresponding to the point where the absolute value of the imaginary part is the maximum.

[0033] Figure 3 This application provides a data diagram illustrating the relationship between characteristic frequency and temperature, and the calculation of activation energy, demonstrating the fitting relationship between characteristic frequency and temperature, and the activation energy value obtained based on the fitting relationship.

[0034] Figure 4 This application provides a method for calculating activation energy using charge transfer impedance, which is used to verify the reliability of activation energy calculation based on characteristic frequency. It shows the fitting results and comparative analysis of impedance parameters with temperature changes. Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments.

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Example 1 This embodiment provides a method for determining the activation energy of a lithium-ion battery. The battery used in this embodiment is a three-electrode lithium-graphite half-cell, and its specific assembly method is as follows: First, a three-electrode battery was assembled, with the reference electrode being a copper wire coated with lithium metal. The graphite anode material was dried in a forced-air drying oven at 80 ℃ for 48 h before use. The separator was made of polyethylene (PE). The electrolyte was a 1 mol / L LiPF6 (EC:DMC = 3:7, volume ratio) electrolyte system (model LB63).

[0038] After assembly, the battery undergoes formation treatment, and the electrode materials are activated by applying an appropriate current, enabling the battery to have normal electrochemical reaction capabilities.

[0039] The activation energy determination method in this embodiment includes the following steps (the results are shown in Figures 2 and 3): S1. Perform sweep impedance testing on lithium-ion batteries at different temperatures to obtain impedance spectrum data at the corresponding temperatures. In this embodiment, the test temperatures are 10 ℃, 20 ℃, 30 ℃, 40 ℃, 50 ℃, and 60 ℃, respectively.

[0040] S2. Based on the impedance spectrum data, obtain the characteristic frequencies at each temperature. Specifically, the frequency corresponding to the maximum absolute value of the imaginary part of the impedance is taken as the characteristic frequency of that temperature. The frequency range of the swept impedance test is 0.01 Hz to 1,000,000 Hz, and the amplitude of the test disturbance signal does not exceed 10 mV to ensure that the test is in the linear region. The characteristic frequencies obtained at 10 ℃, 20 ℃, 30 ℃, 40 ℃, 50 ℃, and 60 ℃ are 7.1 Hz, 15.8 Hz, 39.8 Hz, 70.8 Hz, 158.5 Hz, and 316.2 Hz, respectively.

[0041] S3. Establish the relationship between the characteristic frequency and temperature, and calculate the activation energy and pre-exponential factor of the lithium-ion battery based on this relationship. In this embodiment, a model in which the characteristic frequency and temperature satisfy the Arrhenius relation is used, which is linearized, and the activation energy and pre-exponential factor are calculated based on the slope and intercept of the linearized expression.

[0042] The formula established in this embodiment is y = -7.1x + 27.2.

[0043] The activation energy measured in this embodiment is 59.0 kJ mol. -1 The pre-exponential factor is e 27.2 .

[0044] Example 2 The method for determining the activation energy of a lithium-ion battery in this embodiment is verified by calculating the activation energy using the battery resistance value. The battery used is the same as in Embodiment 1, and the specific steps are as follows, with the difference being: The temperature range used in this embodiment is -25 ℃, -20 ℃, -15 ℃, -10 ℃, -5 ℃ and 0 ℃.

[0045] The formula established in this embodiment is y = -7.2x + 27.1.

[0046] The activation energy measured in this embodiment is 59.9 kJ mol. -1 The pre-exponential factor is e 27.1 .

[0047] Example 3 The preparation method for the lithium-ion battery activation energy determination method in this embodiment uses the same battery as in Example 1, and the specific steps are as follows, except that: Frequency sweep impedance testing was performed on the lithium-ion battery at different temperatures to obtain impedance spectrum data at the corresponding temperatures. The battery used in this embodiment is a three-electrode lithium iron phosphate-graphite full cell, and the operating temperature range is -5 ℃, 0 ℃, 5 ℃, 15 ℃, and 20 ℃.

[0048] The formula established in this embodiment is y = -7.7x + 27.7.

[0049] The activation energy measured in this embodiment is 64.0 kJ mol. -1 The pre-exponential factor is e 27.7 .

[0050] Example 4 The preparation method for the lithium-ion battery activation energy determination method in this embodiment uses the same battery as in Example 1, and the specific steps are as follows, except that: The battery used in this embodiment is a three-electrode lithium iron phosphate-graphite pouch cell, and its operating temperature range is -20℃, -15℃, -10℃, -5℃, and 0℃. The formula established in this embodiment is y = -6.7x + 24.1.

[0051] The activation energy measured in this embodiment is 55.7 kJ mol. -1 The pre-exponential factor is e 24.1 .

[0052] Example 5 The preparation method for determining the activation energy of the lithium-ion battery in this embodiment is basically the same as that in Example 1, except that the positive electrode of the three-electrode soft-pack battery used is a mixture of lithium manganese iron phosphate and ternary cathode, while the negative electrode is still graphite. The temperature range used is 5 ℃, 10 ℃, 15 ℃, 20 ℃, and 25 ℃.

[0053] The formula established in this embodiment is y = -7.6x + 27.4.

[0054] The activation energy measured in this embodiment is 63.2 kJ mol. -1 The pre-exponential factor is e 27.4 .

[0055] Comparative Example 1 The preparation method for determining the activation energy of the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that the method for calculating the activation energy is different. The method for calculating the activation energy in this comparative example is to fit R through an equivalent circuit. ct Establish a formula to calculate the activation energy ( Figure 4 ).

[0056] The formula established in this embodiment is y = -6.2x + 18.5.

[0057] The activation energy measured in this embodiment is 51.5 kJ mol. -1 The pre-exponential factor is e 18.5 .

[0058] Comparative Example 2 The preparation method for determining the activation energy of the lithium-ion battery in this embodiment is basically the same as that in Example 1. The difference is that the method for calculating the activation energy is different. In this comparative example, R is obtained through DRT analysis. ct Establish a formula to calculate the activation energy.

[0059] The formula established in this embodiment is y = -8.0x + 25.1.

[0060] The activation energy measured in this embodiment is 66.5 kJ mol. -1 The pre-exponential factor is e 25.1 .

[0061] The test results of Examples 1-5 and Comparative Examples 1-2 show that the lithium-ion battery activation energy determination method proposed in this application, which is based on the frequency corresponding to the maximum absolute value of the imaginary part of impedance (i.e., characteristic frequency), has good applicability, stability and consistency. It can obtain reliable activation energy data under different battery systems, different temperature ranges and different test configurations (half-cell, full-cell, soft-pack structure, etc.).

[0062] First, as shown in Example 1, in a three-electrode lithium-graphite half-cell system, establishing the Arrhenius relation using characteristic frequencies yields a stable activation energy (59.0 kJ / mol) and pre-exponential factor, proving the feasibility of directly characterizing ion dynamics based on characteristic frequencies. Example 2 conducted verification tests in the low-temperature range (-25 °C to 0 °C), and the activation energy was calculated using the battery resistance (R). Although the calculation method differs from that using characteristic frequencies, the final activation energy (59.9 kJ / mol) is highly consistent with the result of Example 1, demonstrating a good correspondence between this method and the traditional resistance method, further validating the accuracy of the method of this invention.

[0063] Examples 3-5 demonstrate the applicability of the method of the present invention under different cathode systems (lithium iron phosphate, lithium iron phosphate pouch, and lithium manganese iron phosphate ternary hybrid cathodes), different battery structures (three-electrode full cell, pouch three-electrode), and different temperature ranges (-20 ℃ to 25 ℃). The activation energies obtained in each example are 64.0 kJ / mol, 55.7 kJ / mol, and 63.2 kJ / mol, respectively, all falling within the reasonable range of electrode kinetic activation energies. The differences between different electrode systems and different temperature windows can be sensitively distinguished by the characteristic frequency method, indicating that the method can accurately reflect the kinetic differences in battery material systems caused by temperature changes, and has the effectiveness and sensitivity of material evaluation.

[0064] In contrast, Comparative Example 1 and Comparative Example 2 respectively use equivalent circuit fitting for R. ct And DRT analysis to obtain R ct The activation energy was calculated using the method described above. Although both results (51.5 kJ / mol and 66.5 kJ / mol) were within the theoretically reasonable range, they showed significant deviations from the results of Examples 1-5. Furthermore, since both the equivalent circuit fitting and DRT methods involve subjective factors such as model selection, initial parameter setting, and noise processing, the activation energy data fluctuated more significantly. This indicates that traditional methods are more sensitive to the experimenter's experience, and the repeatability and stability of the test results are not as good as the characteristic frequency method of this invention.

[0065] As can be seen from the results of the combined embodiments and comparative examples, the method of the present invention has the following significant features: (1) Strong stability: The activation energy obtained by the characteristic frequency method shows good consistency in different test battery systems and temperature ranges, avoiding the parameter jump and fitting instability that are easy to occur in traditional methods.

[0066] (2) Wide range of applications: Whether it is a half cell or a full cell, a hard-shell or soft-pack structure, or different positive and negative electrode material systems, this method can obtain a stable characteristic frequency and complete the activation energy calculation, which is applicable to a variety of scenarios in battery research and development, production and evaluation.

[0067] (3) The method is simple and has good repeatability: the characteristic frequency can be directly extracted from the impedance imaginary part curve without relying on the equivalent circuit or advanced mathematical analysis tools, which significantly reduces the complexity of the analysis; at the same time, since there is no need for model selection, it also avoids the fluctuation of results caused by human factors and improves the repeatability of data.

[0068] (4) The accuracy of the results has been verified by multiple tests: the resistance method results of Example 2 are in good agreement with the characteristic frequency method results, proving that the method of the present invention has good accuracy and physical significance; the difference between the examples and the comparative examples also confirms the limitations of the traditional fitting method, highlighting the reliable advantages of the present invention in practical applications.

[0069] (5) Significantly enhanced engineering applicability: Due to its simple operation, low equipment requirements, and suitability for automated temperature scanning, this method can be easily applied to high-throughput testing in laboratories, material screening, and production line process monitoring. It is a rapid activation energy determination technology with engineering potential.

[0070] In summary, through systematic verification using multiple embodiments and comparative examples, the lithium-ion battery activation energy determination method proposed in this invention can directly obtain activation energy based on characteristic frequencies, avoiding the complexity and uncertainty of traditional methods. It has significant advantages in terms of accuracy, stability, universality, and engineering usability, and can effectively meet the application needs of multiple fields such as lithium-ion battery kinetic analysis, low-temperature characteristic research, and material development.

Claims

1. A method for determining the activation energy of a lithium-ion battery, comprising the following steps: S1. Perform frequency sweep impedance testing on lithium-ion batteries at different temperatures to obtain impedance spectrum data at the corresponding temperatures; S2. Based on the impedance spectrum data, determine the frequency corresponding to the maximum absolute value of the imaginary part of the impedance as the characteristic frequency value at that temperature; S3. Establish the relationship between characteristic frequency and temperature, and calculate the activation energy and pre-exponential factor of lithium-ion battery based on the relationship.

2. The method for determining the activation energy of a lithium-ion battery according to claim 1, characterized in that: The frequency sweep impedance test has a frequency sweep range of 0.01 Hz to 1,000,000 Hz.

3. The method for determining the activation energy of a lithium-ion battery according to claim 1, characterized in that: When the frequency corresponding to the maximum absolute value of the imaginary part of the impedance falls at the boundary of the frequency scanning range, the frequency scanning range is adjusted and the frequency sweep impedance test is performed again.

4. The method for determining the activation energy of a lithium-ion battery according to claim 1, characterized in that: A functional expression is established that satisfies the Arrhenius relation between the characteristic frequency and temperature. The functional expression is then linearized, and the activation energy and pre-exponential factor are calculated based on the slope and intercept of the linearized expression.

5. The method for determining the activation energy of a lithium-ion battery according to claim 1, characterized in that: The full cell was subjected to swept impedance testing at different temperatures to obtain its characteristic frequency, and the activation energy of the full cell was calculated based on the relationship between the characteristic frequency and temperature.

6. The method for determining the activation energy of a lithium-ion battery according to claim 1, characterized in that: Construct corresponding half-cells for the positive or negative electrode, and perform sweep impedance tests on the half-cells at different temperatures to obtain the characteristic frequencies of the positive or negative electrode, and calculate the corresponding activation energy based on the relationship between the characteristic frequencies and temperature.

7. The method for determining the activation energy of a lithium-ion battery according to claim 1, characterized in that: The swept-frequency impedance test uses an AC disturbance signal with an amplitude not exceeding 10 mV to ensure that the test process is in the linear region.

8. The method for determining the activation energy of a lithium-ion battery according to claim 1, characterized in that: The different temperatures mentioned in step S1 include at least three temperature ranges, and the interval between adjacent temperatures is no greater than 10 °C.

9. The method for determining the activation energy of a lithium-ion battery according to claim 1, characterized in that: The temperature range for the sweep frequency impedance test is -25 ℃ to 60 ℃.

10. The method for determining the activation energy of a lithium-ion battery according to any one of claims 1 to 9, characterized in that: The lithium-ion battery is a lithium-ion battery that uses a lithium-ion intercalation / deintercalation mechanism for charging and discharging.

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